Bidirectional Quasi Z-Source Inverter Fed Induction Motor Drive

Abstract: A novel direct control of high performance bidirectional quasi-Z-source inverter (BQZSI), with optimized controllable shoot-through insertion, to improve the voltage gain, efficiency and to reduce total harmonic distortion is investigated. The most traditional power converters used for adjustable speed drives (ASD) is the voltage source inverter. The VSI usually requires an additional boost converter. This additional converter stage increases cost and complexity and lowers overall efficiency of the power conversion system. Also, the voltage sags can interrupt traditional ASD systems, thus shutting down critical loads and processes. Theoretically, the original Z-source, Quasi-Z-source, and embedded Z-source all have unlimited voltage gain. Practically, however, a high voltage gain (>2 or 3), will result in a high voltage stress imposed on the switches. Every additional shoot-through state increases the commutation time of the semiconductor switches, thereby increasing the switching losses in the system. Hence, minimization of the commutation time by optimal placing of the shoot- through state in the switching time period is necessary to reduce the switching loss. To overcome this problem, a combination of bidirectional quasi-Z-source inverter with a maximum constant boost control with third harmonic injection is proposed. This is achieved by voltage-fed quasi-Zsource inverter with continuous input current, implemented at the converter input side which can boost the input voltage by utilizing the extra switching state with the help of shoot-through state insertion technique. The power flow can be bidirectional by connecting an active switch anti-parellel with the diode in BQ-ZSI. So it can also be used for electrical vehicle applications, since it requires both bidirectional power flow. By using a BQ-ZSI, it is possible to handle the energy in both sides. This bidirectional converter can improve the efficiency of the induction motor. So that the proposed converter have a great future in Electric Vehicle systems. Keywords: Bidirectional quasi-Z-source inverter (BQ-ZSI), adjustable speed drive system application, reverse power flow.